In the oil industry there is in various situations a need to measure the composition or flow rates of individual components of a fluid, which is a mixture of oil and water and possibly gas, flowing in a pipe. Such measurements are needed e.g. to determine what an oil well produces and thus be able to control the production for optimal recovery. Measurements are also needed for monitoring the performance of production separators, control of the injection of chemicals (prevention of the development of scale, corrosion, or hydrate), or for managing the flow regime, when the fluid has to be transported a long distance in a pipeline.
The conventional technique is to separate the fluid in a separator and measure the flow of each of the components separately. During the last few years so-called multiphase meters have also become available, which measure the composition and the flow rates without prior separation [1]. A special case of a multiphase flow is the so-called wet gas flow, which usually means that the GVF (gas void fraction) is roughly GVF>95%. The relative accuracy, which is achievable for the rates of the liquid components, is too low for most applications in the case of a wet gas flow, when measured with multiphase meters.